connection to MySQL leaks after job deleted

[actiontech-bot]

Description

Steps to reproduce the issue:

1. set up a replication job
2. delete the job
3. execute show processlist on source

Describe the results you received:
Found connection to MySQL leaks

Describe the results you expected:

Output of ./dtle version:

(not available)

Additional information you deem important (e.g. issue happens only occasionally):

Additional details (log, config, job config etc):

385c441 should solve the leakage of Binlog Dump thread.

Case 2: Another leakage

mysql> show processlist;
+----+------+--------------------+------+---------+------+----------+------------------+
| Id | User | Host               | db   | Command | Time | State    | Info             |
+----+------+--------------------+------+---------+------+----------+------------------+
|  2 | root | 192.168.2.52:58655 | NULL | Query   |    0 | starting | show processlist |
> |  3 | root | 192.168.2.52:58657 | NULL | Sleep   |   86 |          | NULL             |
+----+------+--------------------+------+---------+------+----------+------------------+

• It is a connection from dtle-src.
• It is Extractor.inspector.db